Hydraulic struts have been used for many years for opening and holding open a door or other closure. Generally, a strut includes two telescoping members and is moveable between a compressed position when the door is closed and an extended position when the door is open. Some struts also provide for locking in the open or extended position.
The speed at which a conventional hydraulic strut extends or compresses is governed by the speed at which hydraulic fluid can enter a chamber and either apply pressure to a moveable piston or fill a vacuum created by the motion of the piston. This fluid flow is created from either the suction action of the retracting piston in a sealed strut, or by an injection system external to the strut.
One disadvantage of conventional hydraulic struts is that the rate of speed at which the strut extends and compresses is the same.
Applications exist where it is desirable to have a strut which opens at one predetermined rate of speed and closes at another. One example is a door which provides access to the personnel carrying area of an aircraft. Doors that can both open rapidly and close slowly allow for rapid and easy exit from the vehicle when the door opens and avoid injuring personnel or damaging items when closing the door. It is also desirable that the strut provide for a mechanism to lock it in the extended or open position.
There exist struts which have variable expansion and compression speeds. These are achieved by using variable flow rate valves which allow for fluid flow at two different speeds, depending on the direction of flow. Rapid opening struts operate by pressurized injection of hydraulic fluid into the strut from an outside source or an injection device. When the strut is compressed, the injected hydraulic fluid is returned to the outside source or discharged from the strut system. A disadvantage of this type of strut is that, because the strut is not sealed and self contained, the hydraulic fluid can become contaminated or leak onto surrounding structures. Another disadvantage is that the addition of an injection device makes the strut system bulkier and more cumbersome than conventional struts.
In view of the above, it should be appreciated that there is still a need for a dampening strut that can open and close at different speeds; is compact, sealed, and self-contained; and can automatically lock in an open position. The present invention satisfies these and other needs and provides further related advantages.